This invention relates generally to echo detection apparatus and more particularly to such a device having a variable frequency transmitter oscillator.
A number of techniques have been proposed for the detection of echo signals in a continuous wave system. A Doppler shift technique is one such technique and detects the radial motion of objects producing reflections in the field of a transmitted signal by comparing the frequency of the transmitted signal to that of the reflected signal. A frequency difference indicates the presence of a moving object in the signal field.
U.S. Pat. No. 3,863,240 to Aaron A. Galvin discloses a continuous wave system in which motion is detected by determining when the received signal level changes in phase or amplitude over a predetermined threshold.
The present invention offers advantages over the well known Doppler detection system in its ability to detect very slow motion of objects in the field of the transmitted signal and to determine the change in positions of objects from one time to a later time. This invention can also detect a radial movement and continuous movement.